1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device. More particularly, the present invention relates to a method for fabricating a semiconductor device wherein a good ohmic contact can be obtained in a plurality of wiring layers composed of an Al film.
2. Description of the Related Art
The "Al film" as used herein refers to a film of aluminum or an aluminum alloy mainly composed of aluminum.
FIGS. 2a through 2c are sectional views illustrating the conventional method for fabricating a semiconductor device. As shown in FIG. 2a, an SiO.sub.2 film 2 and an Al film 3 for a first wiring are formed on an Si substrate 1, and a second SiO.sub.2 film 4 is formed as an interlaminar insulating film. A contact hole 5 is also formed.
By formation of the contact hole 5, the Al film 3 is exposed and an oxide formed by reaction with O.sub.2 in air or an adsorbed material 6 is deposited on the exposed surface of the Al film 3. The presence of the oxide or adsorbed material 6 is an obstacle to formation of a good ohmic contact. Therefore, according to the conventional technique, as shown in FIG. 2b, the oxide or adsorbed material is removed by irradiation with Ar plasma before formation of an upper Al film.
As shown in FIG. 2c, an Al film 7 is formed by the sputtering method and a good ohmic contact is obtained between the Al film 3 and the Al film 7.
As pointed out above, according to the conventional method, the oxide or adsorbed material 6 on the Al film 3 is removed by irradiation with Ar plasma before formation of the Al film 7.
However, as according to the conventional method irradiation with an ion or radical is carried out, the surface of the Al film 3 is roughened and the SiO.sub.2 film 4 is seriously damaged, resulting in formation of a defective element. Especially, in a high-density MOSLSI, since a gate SiO.sub.2 film is broken by the discharge of the electrical charge accumulated, a short circuit is readily formed. Further, where the contact hole 5 has a very small diameter or a very large depth, it is difficult to satisfactorily remove the oxide or adsorbed material 6 due to the insufficient irradiation of the Ar plasma, or to obtain a good contact between the Al films 3 and 7 due to the insufficient penetration of Al into the hole. Therefore, the development of a means for overcoming these disadvantages is eagerly desired.
In "Laser Planarization", Solid State Technology, April 1986, it is disclosed that a metal conductor film, such as of gold, is planarized by irradiation of a dye laser beam. However, this article does not mention any measure for solving the above-mentioned problem.